FR2713759A1 - Optical imaging system for non-contact detection of observed object shape and colour by space-time opto-electronic triangulation - Google Patents

Abstract

The measuring system includes a sub-assembly which illuminates the surface of the object to be measured. This comprises a unidirectional light source (1) and a scanning system providing planar scanning which is a function of time. A second sub-assembly is provided to observe the region illuminated by the scanning beam. The second sub-assembly includes an observation lens (3), a slit array (4) and a mono-element photoelectric detector (5) as well as a linear multi-element photoelectric detector (6). A mechanical support allows the observed object to be moved w.r.t. the observation system. An electronic computer system controls the movement of the object, and the processing of the data collected.

Description

The present invention relates to an optolectronic device of ingul spato-

  temporal for the real-time, contact-free implementation of the surace of objects whose binding and textures as well as any color are arbitrary. It is often necessary to check in progress or at the end of production the dimenions

  industrial parts in order to validate the correct execution.

  The main aspects of a dimensioned measurement are in general: that it be carried out in reduced time, that it can be carried out on surfaces that do not allow contact, that the accuracy of the measurement is compatible with the

rfpfecation considered.

  R & D analysis in 3D metrology, both in terms of physical principles and of their different implementations, shows the two essential limitations encountered in syhems based on geometric triangulation, namely: it is difficult to carry out very large photomeric measurements, the time and the important means of computation necessary to rextractio the coordinates (x, y, z) of all the points measured (typically a few

  thousands to tens of thousands of points per measurement field).

  These two limitations are avoided by the present invention of non-temporal and temporal means which consists in: replacing the photoménic measurements by temporal measurements which are much easier to achieve (clock at 40 MHz), making the observation channel active by having it participate in the coding of

respace of mesre.

  The use of an "active" observation channel makes it possible to overcome the problem of coding ordering error, and the use of a telecentric observation opto reduce the computations.

  x and y coordinate of the mesus points being denied by consucti.

  Only then remains the calculation by interpolation in a matrix of cabrn = io of

coordinates z of the points eurés.

  The object of the present invention is to provide a device for conveniently, without contact, with precion and at a lower cost the external surface of this object.

  Optoelectronic device is based on the physical principle of spatio-triangulation

time.

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  The subject of the present invention is a device for spatiotemporal triangulation intended for the real-time non-contact mediation of the surface of any photometric and photoretic texture object, which comprises: a an optical source generating a ndction ndction nd a bagse system in a plane (X, z), parf itemet synchronized tempore _n, allowing to know at any moment the direction of the picea dnilhn / nnon in the swept plane, ò an afocal optics obso telecentric of the backscattered stream for the object to be measured, at a test chart which associates with the observation plane it is possible to generate n observation directions parallel to each other and to the scanning plane (x, z) i a detec monolment making it possible to acquire a signal representative of the sucoess moments of 6 ssement of the slots by the brush retrodffusé by the surface of the object measured and coming from the point of action current on said object of the brush duminai On the basis of its detachment, the X generated by the scanning system, a linear detector allowing to acquire a repetitive representative record of clearly slits of the target pattern, a perceptual system of The user of the optics of the camera should be placed on the screen of the slots on the multanet detector, a processing die which, for each balyae, can be used to determine the illuminated slots, to accurately measure the successive times of the slots and to assoaer to each fimte eclair f1 nstant ecant him cant, * a software of computation making it possible to determine the altitude Zi of the points acqs on robjet to measure (points corresponding to intersections of the trace sivat x, generated by the scan of the pinca d lmmm mion rdobjet, and observation dctions de fi ned by the slit pattern and afocal roptic telci u), from: - instants ti of each slit F, (from each direction d!) of observation) - data of cabration defined for each me 4 (dirction dobs tion) ls instants of a in tco a has pm am comes., zA mechanical means of locplacement retf (translation or rotation) of robjet to measure in relation to the plan of sweeping and obstruction

(Xz).

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  -3- Particular embodiments of the object of the present invention are described below, by way of example, in relation to the nexes das lese: Figure I represents ledi sdon In Figure 2 represents so In addition to an embodiment of the device according to the invention, FIG. 3 represents the chronogram of acquisition and processing of the symbols.

emitters of detectors (5) and (6).

  FIG. 2 shows a laser source (1) associated with an optic (11) of shaped and focalisaion shape of the luninous brush. At the optical output (I 1) is placed a baly eimpler (2) which is controlled by the electronic module (12) and whose chronization with the rest of equipment is provided by the optoelectronic module (13). This baying beam allows to manage an angular displacement which is characterized in a temporal manner by the illumination beam in the measurement plane, this angular sweep is translated by a displacement of the short-term impact point.

mwurer following the direction x.

  The object to be measured is located inside the field scanned by the pinna diaon and is placed on a motorized table (10) controlled by the tronic module (12) and provides the relational movement of the measuring plane with respect to the object followed by a ypp management has to x direction of pinoeaL's sweeps

  The afocal optic (3) allows, thanks to the slot pattern (4) placed in its focus' ia.

  to manage fixed and paraflix directions of observation between the defissat the coordinates x points to be acquired on the object to be measured, whatever the

corone y and z of said points.

  The transport optics (7), associated with the semi-reflective plate (14), allows both the observer pupil (3) to be imaged on the photoebral detector: mono (5), and to diagnose the target Slots (4) on the multi linMire detects

elements (6).

  The detectors (5) and (6) are connected to the electronic module of ease in form and titration of the signal (S) which tbnst data acquired years to the logcal calc

  the score z points acquired on robjet (9).

  This logiidel uses for the determination of the dimensions z, the calbhtion data (15)

previously stored.

  The device illustrated in Figure 2 operates the next.

  The control electronics (12) associated with the sy on module (13) allows to accurately decorate the application of the angular position of the brush.

  diuminaton from the laser source (1) and loptique (I 1).

BAD ORIGINAL to

  -4- When during the following baying x the impact point of the d9bminato beam on the surface of the robjet to be measured, the directio observation defnies afocale (3) and the fire ire (4), the flow pure red robjet traverse 4. The dux opque and then transported sim a nt by roptique (7) and the semifluring slat (14) to the detector (5), which allows to measure the moments ti of fracism of the slits, and towards the detector (6), which makes it possible to detect having been

illuminated during scanning x.

  The pattern of the determination of the numbers of dectrs (5) and (6), i in FIG. 3, is carried out by the following method by recit (18). During the scan x aner ", the laser source (1) operates at constant power, the detector (5) receives the radio-broadcast by robjet tersant nt the fenrtes

of the target (4).

  The electronics (8) have one of the following operations: detection and storage in a memory of the values of the maximum successes of the analog signal from (5),

  12-bit con-version and sig nalti storage.

  The bare detector element (6) integrates the received stream, during the entire duration of the scan

  aer recorder r state (illuminated or extinguished) of chain of fne.

  During the scan x 'retou', the laser source (1) is off, rectonic (S) it the signal from the mutated detectoreasr (6), f puist this sina and hide a specialized logic deduced ri slits (lit or extinguished), then stoce this

information in a memory fi.

  At the same time, the electronic relay (8) reproduces, by means of a 12-bit analog convector associated with a low-pass filtering, the stored signal duri

aer.

  The sgnati thus restored is divided into cells, each coespomnt u fachisseesnt slits me by the flux revhirized by roet For each cefile, a threshold is defined gce to the prerequisite of the level miml, acquired during the scan ar. This threshold is placed in the vicinity of the slopes. Then the instants of fnissememnt from the threshold to the mounted l and to the descte q2 are mesus pélsén The values il and tj2 measured for each that are emu stored sdqentie nent in a memory t. Finally electronic (8) tumnet aum koicid

  (9) the contents of memories f and tj.

BAD ORIGINIALA 4

  After acquisition of these data by the logicidel (9), the latter performs the calculation of the z coordinates of the peaks while the logic (S) acquires the

next isne.

  The different sequences of the calculation of z are as follows: firstly, the times ti of clearance of the slots are calculated by averaging the times til and t2 my pre dmmx by reqr (8) then the ti ani values obtained are paired, in a table (4, t;) at the first frequencies, the first cleft shows Corrponda t to prmer t, and so on ..., the calculation consists in transforming the table (f, ti), resulting from the pairing, into a table (tz;). This tnsform is made from matrices of calbra * n (15) antinently aqued and which for each 4 associates with a finite number of known z, atam time of tcal cahibration. The aloehm of computation consists, for each one, to look for in the table of cahorking corresponding the preie value of l to issurdlae is tcj then to conceal zi by linear interpolation between tca and tcay-1 z: - - (t, - t. ) + z. <The zi thus are then stored in the 3D matrix (r, y, z) of the states where ir is denoted by the number of the slot F and y is defined by the position of the table

  Motorized (10) los of acquiring the igneous.

  Since all these computations are made during the time required for the acquisition of a new line, the device thus acquires in real time the z-point elevation.

  located on a measuring head in a rthonorned mesh.

  With a scanning period of 30 msec, and a speed of displacement of the table y (5) of 33.333 mm / s, it is posse with the device to measure z x 126 x 126 orthogonally distributed on an object of maximum volume 125 x 125 x 80mm3 in less than 5 socondes and with

  a precision better than 0.01 mm on each point.

  To this end, the device according to the invention is intended particularly for the surface and exterior snubber of objects, and for the control being carried out on a pion line, of the confluence of the shaved parts.

BAD ORIGINAL

  According to another embodiment, the mujltidelement detector (6) is read at a high

  rate, whenever a maximum is detected on the signal t from the detector (5).

  According to another embodiment, the values of the maxima detected on the signal t coming from the detector (5) during the nth scan x serve to modulate the power nmise by the source (1) during the (n + 1) th scan x so as to obtain a quasi-uniform energy ripening of the maximuns and thus to satisfy

albedo variations of the object.

  According to another embodiment, the sampling step on the object to be evaluated is

  not constituting so as to be adapted to the geometry of said object.

BAD ORIGINAL

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Claims (6)

  1. Spatio-temporal optoelectronic triangulation device intended for the real-time, non-contacting use of the surface of photometric and colorimetric texture objects, caacti in that it comprises: an optical source (1) generating a brush 'dumination d oel a scanning system (2) in a plane (x, z), perfectn temporally, allowing to know at any moment the direction of the pinnacle of i nation in the plane scanned, At an optical telecentric afocale (3) observation of the backscattered stream by robjet to be measured, has a test pattern of n slots (4) which associated with roptique of observafion (3) allows geniérr n directions of observation parallel to raxe z and coplaires to scan plane (x, z) , To a monoelement detector (5) for acquiring a signal representative of the successive moments of crossing the fites by the brush retrodiffused by the measured jetjet surface and coming from the current incident point on said object of the illuminated brush, during its displacement along the axis X generated by the scanning system (2), to a linear multielement detector (6) making it possible to acquire a signal representative of illumination detection of the slots of the target (4) during the scanning, an optical system (7) permta: to image the observation roptic pupil (3) on the mooléent detector (5) a to imager the slit pattern (4) on the linear detector multielnent (6) , a processing electonic (8) allowing for each scan, to determine the illuminated slots, to accurately measure the successive instants ti men slits and to associate each illuminated slot f the instant of illumination ti corresponding, - a calculation software (9) for determining altitude; points on robjet i menaur (points corresponding to the intsections of the following trace x, generated by the scanning of the iuminatio brush on the object, and observaion ctions defined by the slit pattern), from: * moments reci ti of each fete 4 (of each direction of observation) calibration data (15) defining for each slot f (direction of observation) tcafi illumination instants corcxmdant at frightening altitudes known, ZcWj To mechanical means (10) relative displacement (translation or roation) of robjet i measure with respect to the common plane of scanning and obsevation (x, z) BAD ORIGINAL.9   -8- 2. Device according to claim 1, characterized in that the scanning system (2) consists of a galvanometric mirror managing a reciprocating movement of the brush dillnination   3. Device according to claims I and 2, characterized in that:   during the forward x-scan, the values of the successive maxiunm of the analog signal t i resulting from the detector (5) are measured and stored while the complete signal t i is digitized and stored, A during the x-return scan, the complete signal t i, derived from The detector (5), stored during the forward scan, is decoded and broken down into a cell. For each cell, a threshold is defined from the value of the maximum composite measured to be scaled. The moments of crossing this threshold by the restored signal know how to calculate the instant of famhisslet ti of the slot coaesponda i la cell considered.   4. Device according to claims I and 2 characterized in that the detector   multielement (6) is read at high speed, whenever a maximum is detected   on the signal ti from the detector (5).   5. Device according to claims I and 2 characterized in that the values of the   maxima detected on the signal ti coming from the detector (5) during the neime scan x serve to modulate the power emitted by the source (1) during the (n + 1) th scan x so as to obtain a quasi-umfome energy distribution of the maximums,   and amsi to get rid of variations of robjet albedo.   6. Device according to the preceding claims characterized M cen that not   Sampling on a robjet to be measured is not constant so as to be adapted to the geometry of said object. BAD ORIGINAL)